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An explosion experiment was conducted in the Barre granite of central Vermont during July 2008 using five explosions and three different types of explosives with a wide range of velocities of detonation. Black powder, heavy ANFO, and Composition B were used to generate increasing amounts of borehole pressure and different types of rock damage. The velocity of detonation was found to affect the peak particle velocities (PPV). ANFO produced the largest PPV, while the Composition B PPVs were slightly lower. Black powder produced much lower PPV, likely due to it deflagrating rather than truly detonating. An equation was fit to the data for predicting the PPV from a confined blast in the Barre granite using two methods, including true vector summation. Vector summation provides a more accurate measure of particle velocity. We found the frequency of the PPV decreases with increasing distance from the blast, and therefore extra care must be taken for large blasts where lower frequency energy may exceed vibration limits at greater distances. |
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